A variety of punch and die assemblies have been previously provided for rounding the corners of a piece of sheet metal by shearing off the corners of the sheet. Ordinarily such a machine will provide only a single corner radius. However, U.S. Pat. No. 3,516,317 describes a punch and die assembly that includes an aligned die and punch each having a plurality of longitudinally spaced apart arcuate cutting edges in side by side relationship with each cooperating pair being of a different size, i.e., different radius from the other pairs. A workpiece is placed between the cutting edges of the desired radius to remove the corner portions and thereby provide a round corner of the selected radius. The present invention is an improvement on the apparatus described in the patent. One of the important shortcomings of the prior device was the requirement for using it in conjunction with a conventional punch press. Thus, to operate the apparatus, it had to be set on the table of the punch press below the power driven reciprocating head. In addition to the large size and bulk of the equipment, the necessity for providing a punch press requires a substantial investment, typically about $15,000. Thus, one objective of the invention is to provide a machine tool that is ready to go at a moment's notice and without having to be set up for operation. However, if it is attempted to make the machine self-actuating, there is a tendency for the punch to tilt when the shearing operation is conducted at either extreme end of the machine. A further shortcoming of prior devices was the possibility for the punch to be deflected or bend under stress. A further deficiency was the possibility for incorrectly positioning the guide bar used to align the work. This resulted from the lack of any reliable provision for preventing locating pins from being inadvertently placed in the wrong locating holes when the guide bar was used.
These and other more detailed and specific deficiencies and provisions for overcoming them will be apparent to those skilled in the art through an understanding of the following summary and detailed description in which the invention is set forth by way of example with reference to the drawings.